Compile fix with gcc 4.9

Change-Id: I1e31529081002f3bdfe4be7b610ec6ec8e6139df
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/projectexplorer/iprojectpanelfactory.h

@@ -38,6 +38,8 @@
 #include <QIcon>
 #include <QWidget>
 
+#include <functional>
+
 namespace ProjectExplorer {
 class Project;
 class Target;